The present invention relates to an article with an antifogging film, which is useful for windows, mirrors and the like in various fields such as architectural, industrial and automotive ones, and a process for producing the article.
In recent years, there have been proposals of forming photocatalytic films on the substrate surface for providing hydrophilicity and antifogging property.
Japanese Patent Laid-open Publication JP-A-5-253544 discloses a process for producing a plate-like member with deodorizing function by applying a glaze to a substrate and then by spraying an anatase-type TiO2 powder to the glaze layer.
JP-A-7-232080, which corresponds to U.S. Pat. Nos. 6,027,797 and 5,853,866, discloses a multifunctional material with photocatalytic function, prepared by forming a binder layer on a substrate and then by forming a photocatalytic layer of photocatalytic particles on the binder layer.
JP-A-9-59042 discloses a transparent substrate with an antifogging coating containing photocatalytic titania particles.
JP-A-52-101680 discloses an antifogging agent containing polyacrylic acid, surfactant and a solvent (water and/or alcohol).
Japanese Patent Examined Publication JP-B-5-67330, which corresponds to JP-A-1-38103, discloses a hydrophilic porous film and a process for producing the same. This film is made of a hydrophobic polymer. The external surface and the pore surfaces of the film are coated with a coating of a polyvinyl alcohol/vinyl acetate copolymer and then with a coating of a hydrophilic polymer.
JP-A-10-212471 discloses an antifogging agent containing polyvinyl alcohol, tetramethoxysilane, and hydrochloric acid as a catalyst for polycondensation of these compounds.
JP-A-11-84102 discloses an antifogging coating film and an optical article with this film. This antifogging coating film has (1) a water-absorbing film formed on a substrate and (2) a porous film formed on the water-absorbing film.
JP-A-5-51471 discloses a laminate prepared by forming a curable coating film on a substrate. At least a surface layer portion of the substrate is made of a polymer having xe2x80x94Pxe2x95x90Nxe2x80x94 skeleton.
JP-A-6-157794 discloses an antifogging agent containing a polyvinyl acetal resin.
JP-A-6-158031 discloses a first antifogging article prepared by forming on a substrate an antifogging layer of a polyvinyl acetal resin having a degree of acetalization of 2-40 mol %. This publication further discloses a second antifogging article prepared by forming a water-soluble resin layer on a substrate and then the antifogging layer.
JP-A-9-136374 discloses an antifogging resin article prepared by forming on a resin substrate a first layer containing hydrophilic inorganic fine particles and a coupling agent and then by forming on the first layer a second layer made of a hydrophilic resin and/or a surfactant.
It is an object of the present invention to provide an antifogging article which is superior in antifogging property and abrasion resistance.
It is another object of the present invention to provide a process for producing such antifogging article.
According to a first aspect of the present invention, there is provided a first antifogging article comprising a substrate; and an antifogging film covering said substrate. This antifogging film comprises a water-absorbing organic polymer and an inorganic substance and has a water repellent finishing on a surface of said antifogging film.
According to the first aspect of the present invention, there is provided a first process for producing an antifogging article, comprising:
preparing a first coating solution by dissolving a water-absorbing organic polymer and a silicon-containing compound in a solvent;
applying said first coating solution to a substrate, thereby forming thereon a first precursory film;
drying said first precursory film into an antifogging film;
applying a second coating solution to said antifogging film, thereby forming a second precursory film on said antifogging film; and
drying said second precursory film into a water repellent film.
According to a second aspect of the present invention, there is provided a second antifogging article comprising:
a substrate;
a water-absorbing, antifogging film covering said substrate, said antifogging film comprising:
(a) a polyvinyl acetal resin having a degree of acetalization of not greater than 10 mol %; and
(b) a hydrolysate or partial hydrolysate of an alkylsilylisocyanate represented by the general formula R2nSiR14xe2x88x92n. where R1 is an alkyl group having a carbon atom number of 1 or 2, R2 is an isocyanate group, and n is 1 or 2; and
a water-permeable, protective film covering said antifogging film.
According to the second aspect of the present invention, there is provided a second process for producing an antifogging article, comprising:
(a) providing a substrate;
(b) preparing a first coating liquid by adding a polyvinyl acetal resin and an alkylsilylisocyanate to a solvent, said polyvinyl acetal resin having a degree of acetalization of not greater than 10 mol %, said alkylsilylisocyanate being represented by the general formula R2nSiR14xe2x88x92n where R1 is an alkyl group having a carbon atom number of 1 or 2, R2 is an isocyanate group, and n is 1 or 2;
(c) applying said first coating liquid to said substrate, thereby forming a first precursory film on said substrate;
(d) drying said first precursory film into a water-absorbing, antifogging film;
(e) applying a second coating liquid containing an alkylsilylisocyanate to said antifogging film, said alkylsilylisocyanate being represented by the general formula R2nSiR14xe2x88x92n where R1 is an alkyl group having a carbon atom number of 1 or 2, R2 is an isocyanate group, and n is 1 or 2, thereby forming a second precursory film on said antifogging film; and
(f) drying said second precursory film into a water-permeable, protective film.
The first and second antifogging articles can respectively be produced by the first and second processes.
The above-mentioned first antifogging article of the invention is superior for a long time in antifogging property, durability (particularly abrasion resistance) and transparency, has no image distortion, no defects such as cracks, nor damage to the color tone of its substrate. The first antifogging article can efficiently be produced by the first process with a low production cost and a high productivity. The first antifogging article can be used for various indoor and outdoor glass articles such as architectural window panes, bathroom mirrors, and automotive door mirror and window panes.
The antifogging film of the first antifogging article is superior in antifogging property due to the inclusion of a water-absorbing organic polymer therein. When water drops fall on the antifogging film, they are absorbed by this film until the maximum of the water-absorbing capacity of the organic polymer. With this, it is possible to maintain the antifogging property of this film. Furthermore, even if it exceeds the maximum of the water-absorbing capacity, a uniform water film can be formed on the antifogging film. With this, it is also possible to maintain the antifogging property of the film. However, a film made of only a water-absorbing organic polymer not according to the invention is inferior in water resistance and mechanical strength and can not be expected to have a superior chemical durability. In contrast, according to the first aspect of the present invention, the antifogging film contains an inorganic substance (amorphous silica) in addition to a water-absorbing organic polymer. With this, the antifogging film is unexpectedly substantially improved in water resistance, chemical durability and adhesion to the substrate. Furthermore, according to the first aspect of the invention, it is preferable that the antifogging film is coated with a water repellent film as a protective film. With this, the surface of the antifogging article is lowered in free energy (i.e., considerably lowered in coefficient of kinetic friction). Therefore, it becomes possible to considerably improve the antifogging article in abrasion resistance. Furthermore, it is preferable that the water repellent film has an ultra-thin thickness of not greater than 10 nm and a porous or incompact structure. This structure can be obtained by drying the second precursory film at a second temperature of 70-120xc2x0 C. in the first process. In other words, the water repellent film can be a porous, monomolecular film. Thus, the water repellent film can provide air permeability and water permeability through pores of this film. Therefore, even if the antifogging film is coated with the water repellent film, the antifogging film is not impaired in water absorption or adsorption thereby and in water release or desorption therefrom. Thus, the antifogging article can be superior in antifogging property for a long time.
As stated above, the first antifogging article can be produced by the first process. In this process, the first precursory film is dried into an antifogging film having a so-called composite or inhomogeneous structure where an amorphous silica, derived from the silicon-containing compound of the first coating solution, exists as a matrix in a manner to surround the water-absorbing polymer. With this composite structure, the antifogging film is improved in mechanical strength, chemical durability, water resistance and the like.
In the antifogging film of the first antifogging article, the organic polymer and the silica (inorganic substance) are respectively preferably in amounts of 95-99.5 wt % and 0.5-5.0 wt %, based on the weight of the antifogging film. If the silica content is less than 0.5 wt %, the antifogging film may be insufficient in water resistance and chemical durability. If the silica content exceeds 5.0 wt %, the antifogging film may become inferior in water absorption and antifogging property. The silica content is more preferably from 1.0 to 2.5 wt %. The antifogging film may contain titania, zirconia, alumina and the like, in addition to the silica.
The antifogging film of the first antifogging article has a thickness of preferably 2-10 xcexcm, more preferably 5-7 xcexcm. If it is less than 2 xcexcm, the film may become insufficient in water absorption capability. If it is greater than 10 xcexcm, the film may become inferior in water or air permeability. With this, the rate of water release from the antifogging film may become too slow. Furthermore, the antifogging film may have an opaqueness (white color) with a thickness greater than 10 xcexcm.
As stated above, the antifogging film of the first antifogging article has a water repellent finishing on its surface. This finishing is preferably a water repellent film, but is not limited to the same. It is preferable that the water repellent film has a thickness of not greater than 10 nm. If it is greater than 10 nm, it may become difficult to have a sufficient water adsorption and desorption through the water repellent film. With this, the antifogging article may become inferior in antifogging property.
In the first process, examples of the organic polymer of the first antifogging article are hydroxypropyl cellulose, polyvinyl alcohol, polyvinyl acetal, polyvinyl pyrrolidone, and polyvinyl acetate. Examples of the silicon-containing compound for providing the silica in the antifogging film are tetraethoxysilane, tetramethoxysilane, monomethyltriethoxysilane, monomethyltrimethoxysilane, dimethyldimethoxysilane, and dimethyldiethoxysilane. It is optional to add at least one compound selected from aluminum alkoxides, titanium alkoxides, zirconium alkoxides, aluminum acetylacetonates, titanium acetylacetonates, zirconium acetylacetonates, and zirconium chloride, to the first coating solution, in order to make the antifogging film contain at least one of alumina, titania and zirconia.
In the first process, the raw material of the water repellent film is not particularly limited. Its preferable examples are methylsilicon triisocyanate, dimethylsilicon diisocyanate, trimethylsilicon isocyanate, and fluoroalkyltrimethoxysilanes.
In the first process, the total solid matter concentration of each of the first and second coating solutions may be adjusted to about 1 to about 5 wt %. The viscosity of the first and second coating solution may be adjusted to about 0.002 to 0.01 Nxc2x7s/m2.
In the first process, the first precursory film is dried at a temperature of preferably about 90-150xc2x0 C., more preferably about 110-130xc2x0 C., for a period of time of preferably about 10-30 minutes, more preferably about 15-20 minutes. The second precursory film is dried at a temperature of preferably about 70-120xc2x0 C., more preferably about 100-110xc2x0 C., for a period of time of preferably about 5-30 minutes, more preferably about 15-20 minutes. If these drying temperatures are lower than the respective preferable lowest temperatures, the evaporation of the solvent may become insufficient. Thus, the antifogging film and the water repellent film may become insufficient in water resistance, mechanical strength and/or chemical durability. Drying temperatures higher than the respective preferable highest temperatures do not cause particular disadvantages nor particular advantages, as compared with the above-mentioned ranges.
The second antifogging article is superior for a long time in antifogging property, wiping resistance and abrasion resistance, particularly when the antifogging film is coated with a water-permeable, protective film having a thickness of 3-10 nm. The antifogging film of the second antifogging article is superior in strength, since a cross-linking can be formed by a reaction between hydroxyl group of the polyvinyl acetal resin and the isocyanate group of the alkylsilylisocyanate. Similar to the first antifogging article, the second antifogging article can also widely be used for automobiles and mirrors. Furthermore, the first and second antifogging articles can respectively be produced by the first and second processes at relatively low drying temperatures. Therefore, it is possible to partially or entirely coat a substrate, to which a high temperature drying is not desirable, such as a glass plate already formed into a mirror or an automotive glass pane already bent and shaped, thereby producing the first or second antifogging article.
As stated above, the antifogging film of the second antifogging article contains a first essential constituent, a polyvinyl acetal resin having a degree of acetalization of not greater than 10 mol %. With this, the antifogging film becomes superior in antifogging property and transparency. If its degree of acetalization is greater than 10 mol %, the resulting antifogging film may become inferior in antifogging property. A second essential constituent of the antifogging film is a hydrolysate or partial hydrolysate of an alkylsilylisocyanate represented by the general formula R2nSiR14xe2x88x92n where R1 is an alkyl group having a carbon atom number of 1 or 2, R2 is an isocyanate group, and n is 1 or 2. The amount of the second constituent in the antifogging film is preferably of 1-5 wt %, based on the total weight of the first and second constituents. If it is less than 1 wt %, the antifogging film may become inferior in strength and wiping resistance. If it is greater than 5 wt %, the antifogging film may become inferior in antifogging property.
In the first and second processes, the solvent for preparing the first coating solution (liquid) is preferably a mixture of water and at least one compound selected from (1) alcohols (particularly lower alcohols) such as methanol, ethanol, propanol, ethylene glycol, propylene glycol and hexylene glycol, (2) esters such as ethyl acetate, butyl acetate and amyl acetate, and (3) cellosolves such as methyl cellosolve, ethyl cellosolve and butyl cellosolve. Of these, it is preferable to select a suitable one or mixture of at least two, in view of the evaporation rate of the first coating solution (liquid) and/or viscosity of the first precursory film. Furthermore, it is optional to add suitable amounts of a silane coupling agent (e.g., methacryloxypropyltrimethoxysilane) and a methyl silicone (e.g., dimethyl silicone) as a leveling agent.
In the first and second processes, the manner of applying the first or second coating solution (liquid) is not particularly limited. For example, it can be selected from spin coating, dip coating, reverse coating, flexography, roller coating, curtain coating, nozzle coating, spraying and screen printing.
In the second process, the first precursory film is dried at a temperature of preferably 90-150xc2x0 C. for a period of time of preferably 30-60 minutes. With this, most of the solvent evaporates, and at the same time the hydrolysate or partial hydrolysate of the alkylsilylisocyanate becomes a matrix of the antifogging film. The antifogging film of the second antifogging article has a thickness of preferably about 3-10 xcexcm. If it is less than 3 xcexcm, the antifogging film may become inferior in antifogging durability. If it is greater than 10 xcexcm, the antifogging article may have an optical distortion in connection with the external appearance.
In the second process, it is possible to use an alkylsilylisocyanate represented by R2nSiR14xe2x88x92n where R1, R2 and n are defined as above, for preparing the water-permeable, protective film. In this film, the alkylsilylisocyanate can be in the form of its hydrolysate or partial hydrolysate. In the preparation of the second coating liquid, the alkylsilylisocyanate can be added to a solvent (e.g., ester or hydrocarbon). Furthermore, it is optional to add a leveling agent. The second precursory film can be dried at a relatively low temperature of 90-120xc2x0 C. for a period of time of 10-60 minutes. With this, most of the solvent may evaporate, and at the same time the hydrolysate or partial hydrolysate of the alkylsilylisocyanate may turn into a hardened film. The second antifogging article is improved in scratch resistance and wiping resistance due to the use of the water-permeable, protective film.
The water-permeable, protective film of the second antifogging article has a thickness of preferably 3-10 nm in order to have a sufficient water permeability. If it is less than 3 nm, the antifogging article may become inferior in abrasion resistance and wiping resistance. If it is greater than 10 nm, water permeability of the film may become inferior. With this, the antifogging article may become inferior in antifogging property.
In the first and second processes, the substrate is not limited to particular materials. It may be selected from glass, resin, metal and ceramic, as long as it does not deteriorate by the dryings. It is typically a glass plate, which can be selected from float glass plates for automotive, architectural and industrial uses, clear and various color glass plates of green, bronze and other colors, various functional glass plates, tempered glass plates, laminated glass plates, double-layered glass plates, and flat and bent glass plates. The glass plate may have a thickness of about 1.0-12 mm. In fact, it is preferably about 3.0-10 mm for architectural use and about 2.0-5.0 mm for automotive use.
The following nonlimitative examples are illustrative of the present invention. In fact, Examples 1-1 to 1-10 are illustrative of the first aspect of the present invention, and Examples 2-1 to 2-4 are illustrative of the second aspect of the present invention.